1. Field of Invention
The present invention pertains to the field of instrumentation. More particularly, this invention relates to time coordination among instruments.
2. Art Background
An instrumentation system typically includes a set of instruments which are adapted to obtain measurements in an environment of interest. An example of an instrumentation system is a test system which usually includes a set of instruments that obtain measurements pertaining to a system or device under test. Examples of instruments include volt meters, oscilloscopes, signal generators, and logic analyzers to name a few examples.
Coordination among the measurements obtained by instruments in a typical prior instrumentation system is usually accomplished by applying trigger signals to the instruments whenever measurements are desired. For example, if it is desired that instrument A obtain a measurement at time t0 and that instrument B obtain a measurement at time t1 then a trigger signal is applied to instrument A at time t0 and a trigger signal is applied to instrument B at time t1.
It is often desirable in an instrumentation system to provide time correlation among the obtained measurements. Prior instrumentation systems typically correlate measurements in time by controlling the timing of the trigger signals applied to the instruments. Continuing with the above example, if it is desired to correlate measurements to time t0, then trigger signals may be applied to both instruments A and B at time t0 and the resulting measurements associated to time t0.
Unfortunately, the precision of time correlation in such a prior instrumentation system is usually hindered by a variety of factors. For example, the signal lines that carry trigger signals to different instruments usually create different propagation delays. In addition, the internal circuitry in different instruments usually have different latencies between a time a trigger signal is received and a time that a measurement is performed. Moreover, the engineering effort needed to compensate for such factors usually increases the overall cost of providing precise time coordination of measurements in prior instrumentation systems.
An instrumentation system is disclosed which provides relatively precise time correlation among obtained measurements without dependence on trigger signal timing. An instrumentation system according to the present teachings includes a set of instruments each having a clock and an event buffer for periodically logging a data record. Each data record includes a set of measurement data and a time-stamp obtained from the corresponding clock. The instrumentation system includes mechanisms for maintaining a synchronized time in the clocks and mechanisms for stopping the logging in the event buffers in response to an event of interest. Once event logging is stopped, the data records in the event buffers may be correlated using their time-stamps and a time-stamp associated with the event of interest. The precision of time correlation depends on the precision of clock synchronization rather than the precision of trigger signal timing as in prior systems.
Other features and advantages of the present invention will be apparent from the detailed description that follows.